1. Field of the Invention
This invention relates to a multi-speed planetary drive axle assembly and, more specifically, to an improved system for lubricating the differential mechanism and planetary gear assembly within a substantially enclosed differential case.
2. Description of the Prior Art
U.S. Pat. No. 3,413,873 which issued to L. A. Bixby on Dec. 3, 1968 discloses a two speed planetary drive axle of the type to which the present invention is particularly applicable. The Bixby patent discloses a sleeve type sun gear which is axially movable between a high speed position where the sun gear sleeve is locked in position to rotate with the planetary gear assembly and a low speed position where the sleeve is locked against rotation relative to the axle housing. Planetary pinion gears rotatably mounted on shafts carried by a differential cage are meshed with the sun gear and an internal ring gear rigid with the differential case. The differential mechanism and the planetary gear assembly are substantially enclosed by the differential case which is rotatably mounted to a differential carrier.
The axle housing is fluid tight and a pool or sump of liquid lubricant is provided for the purpose of lubricating the drive assembly as the lubricant is splashed about the housing by the moving parts. This has proven to be an effective means of lubricating those parts of the drive assembly which are exposed to the lubricant. The differential case shields the differential mechanism and the planetary gear assembly from the lubricant splashed about the axle housing and presents a special problem with respect to lubricating the moving parts within the differential case. The problem is not merely one of providing lubricant to the interior of the differential case but rather to provide a continuous flow of lubricant through the case at such a rate as to prevent the temperature of the lubricant and moving parts within the differential case from increasing to an undesirable level.
U.S. Pat. No. 2,178,900 which issued to C. E. Starr on Nov. 7, 1939 discloses a lubricating system for a multi-speed planetary drive axle. The Starr patent discloses a lubricating system in which lubricant is introduced to the interior of a differential case by means of inlet passages provided through one end wall of the differential case and discharged through an outlet passage formed by a groove cut between the sun gear sleeve and the internal surface of a boss rotatably mounting one end of the differential case on the sleeve. Starr discloses that lubricant will pass from the inlet passages through the differential case and then through the outlet passage where it is returned to the axle housing. However, the Starr discharge passage is provided at the outer surface of the sun gear sleeve which is located radially inward of the differential case wall. In operation, lubricant within the differential case would be moved by centrifugal force toward the outer wall of the rotating differential case. Such movement would be in a radially outward direction away from the sun gear sleeve and the discharge passage with the result that little if any lubricant would be discharged to the axle housing before the differential case became almost full of lubricant. The rate of lubricant flow through the differential case is also limited by the location of the Starr discharge passage.